This invention relates to a synthetic resin bumper for a motorcar.
A conventional bumper has been known having a shock absorbing member made of a foamed synthetic resin and a backup beam made of a soft steel plate. The backup beam is a hollow beam member with a constant depth. The shock absorbing member has either a constant depth along its entire length or is largest at the middle part thereof. The shock absorbing member is attached to a front surface of the backup beam (Japanese Patent Kokai Sho No. 55-79726, Japanese Utility Model Kokai Sho No. 55-53645). It has been usual with this type bumper that the shock absorbing member is arranged to be sufficiently shock absorbing that, even when a pendulum strikes a blow at the same at a speed of below 8 km/h, the absorbing member can prevent the backup beam from permanently deforming.
Thus, when such a foamed material as polypropylene, polyurethane or the like is used for making the shock absorbing member having the foregoing degree of shock absorption, the foaming ratio of the foam material has to be restrained to a comparatively low value. Consequently, the resultant foam product becomes comparatively large in weight. In addition, the backup beam thereof is also comparatively large in weight because the same is made of a steel material. This results in the problem that the bumper is large in weight, resulting in increase in consumption of fuel of the vehicle on which it is mounted.